SHA-256 Hash example on mbed OS

File content as of revision 83:9f7b1df6f95a:

/*
 *  Hello world example of using the hashing functions of Mbed TLS
 *
 *  Copyright (C) 2016, Arm Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/*
 * This program illustrates various ways of hashing a buffer.
 * You normally need only one of these two includes.
 */
#include "mbed.h"
#include "mbedtls/sha256.h" /* SHA-256 only */
#include "mbedtls/md.h"     /* generic interface */

#if DEBUG_LEVEL > 0
#include "mbedtls/debug.h"
#endif

#include "mbedtls/platform.h"

#include <string.h>

static void print_hex(const char *title, const unsigned char buf[], size_t len)
{
    mbedtls_printf("%s: ", title);

    for (size_t i = 0; i < len; i++)
        mbedtls_printf("%02x", buf[i]);

    mbedtls_printf("\n");
}

static const char hello_str[] = "Hello, world!";
static const unsigned char *hello_buffer = (const unsigned char *) hello_str;
static const size_t hello_len = strlen(hello_str);

static int example()
{
    mbedtls_printf("\n\n");

    /*
     * Method 1: use all-in-one function of a specific SHA-xxx module
     */
    unsigned char output1[32]; /* SHA-256 outputs 32 bytes */

    /* 0 here means use the full SHA-256, not the SHA-224 variant */
    mbedtls_sha256(hello_buffer, hello_len, output1, 0);

    print_hex("Method 1", output1, sizeof output1);


    /*
     * Method 2: use the streaming interface of a specific SHA-xxx module
     * This is useful if we get our input piecewise.
     */
    unsigned char output2[32];
    mbedtls_sha256_context ctx2;

    mbedtls_sha256_init(&ctx2);
    mbedtls_sha256_starts(&ctx2, 0); /* SHA-256, not 224 */

    /* Simulating multiple fragments */
    mbedtls_sha256_update(&ctx2, hello_buffer, 1);
    mbedtls_sha256_update(&ctx2, hello_buffer + 1, 1);
    mbedtls_sha256_update(&ctx2, hello_buffer + 2, hello_len - 2);

    mbedtls_sha256_finish(&ctx2, output2);
    print_hex("Method 2", output2, sizeof output2);

    /* Or you could re-use the context by doing mbedtls_sha256_starts() again */
    mbedtls_sha256_free(&ctx2);

    /*
     * Method 3: use all-in-one function of the generice interface
     */
    unsigned char output3[MBEDTLS_MD_MAX_SIZE]; /* Enough for any hash */

    /* Can easily pick any hash you want, by identifier */
    const mbedtls_md_info_t *md_info3 = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);

    if (md_info3 == NULL)
    {
        mbedtls_printf("SHA256 not available\n");
        return 1;
    }

    int ret3 = mbedtls_md(md_info3, hello_buffer, hello_len, output3);

    if (ret3 != 0)
    {
        mbedtls_printf("md() returned -0x%04X\n", -ret3);
        return 1;
    }

    print_hex("Method 3", output3, mbedtls_md_get_size(md_info3));


    /*
     * Method 4: streaming & generic interface
     */
    unsigned char output4[MBEDTLS_MD_MAX_SIZE]; /* Enough for any hash */

    const mbedtls_md_info_t *md_info4 = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);

    if (md_info4 == NULL)
    {
        mbedtls_printf("SHA256 not available\n");
        return 1;
    }

    mbedtls_md_context_t ctx4;

    mbedtls_md_init(&ctx4);

    int ret4 = mbedtls_md_init_ctx(&ctx4, md_info4);
    if (ret4 != 0)
    {
        mbedtls_printf("md_init_ctx() returned -0x%04X\n", -ret4);
        return 1;
    }

    mbedtls_md_starts(&ctx4);

    /* Simulating multiple fragments */
    mbedtls_md_update(&ctx4, hello_buffer, 1);
    mbedtls_md_update(&ctx4, hello_buffer + 1, 1);
    mbedtls_md_update(&ctx4, hello_buffer + 2, hello_len - 2);

    mbedtls_md_finish(&ctx4, output4);
    print_hex("Method 4", output4, mbedtls_md_get_size(md_info4));

    /* Or you could re-use the context by doing mbedtls_md_starts() again */
    mbedtls_md_free(&ctx4);


    mbedtls_printf("\nDONE\n");

    return 0;
}

int main() {
    int exit_code = MBEDTLS_EXIT_FAILURE;

    if((exit_code = mbedtls_platform_setup(NULL)) != 0) {
        printf("Platform initialization failed with error %d\n", exit_code);
        return MBEDTLS_EXIT_FAILURE;
    }

    exit_code = example();
    if (exit_code != 0) {
        mbedtls_printf("Example failed with error %d\n", exit_code);
        exit_code = MBEDTLS_EXIT_FAILURE;
    }

    mbedtls_platform_teardown(NULL);
    return exit_code;
}